1. Field of the Invention
The invention is directed to a position sensor, particularly a rotary position sensor, with or without integrated signal-conditioning electronics.
2. Description of Related Art
Rotary position sensors are instrumental in the control of rotary motion. The sensors are used for position feedback and position information.
Sensor resolution, accuracy, cost, and size are key specifications in choosing a rotary sensor. There are several different types of rotary position sensors in general use. These include, but are not limited to, resolvers, encoders (optical and magnetic), Hall-effect sensors and potentiometers.
Resolvers have several disadvantages. They are bulky, difficult to manufacture, and relatively expensive for precision units, namely, over $500.
The main disadvantage of encoders is that they provide only discrete position information. In other words, encoders output position information only in terms of discrete positions, steps, or pulses per revolution (PPR), and the relative spacing among the positions, steps, or PPR determines the resolution of an encoder. Low-resolution encoders can be relatively inexpensive, namely, approximately $50, but highly accurate and absolute encoders can be very expensive. Some laser encoders offer high accuracy and resolution, but at a cost of several thousand dollars.
Hall-effect devices are relatively inexpensive, but they are not very accurate in a linear mode. Hall devices also are affected by fluctuating magnetic fields and require a fixed air gap.
Potentiometers are relatively inexpensive. However, they are electrically noisy.
Each of these sensors also requires external electronics to signal-condition the raw sensor output. These sensors thus have a disadvantage in that the external electronics are not incorporated inside the sensor housing.
Integrating the electronics would require another manufacturing procedure, increase device cost and make the sensors larger and more bulky. In some cases, such as for Hall-effect sensors, including the signal conditioning electronics would possibly more than double the size of the original sensor. There would also be the problem of interference between the signal-conditioning electronics and other components of the sensor.
U.S. Pat. No. 6,246,228, entitled Non-contact Linear Actuator Position Sensor and Controller Insensitive to Air Gap Between Armature and Magnetic Bracket, whose disclosure is incorporated by reference in its entirety into the present disclosure, teaches a position sensor or controller that generates a response signal in existing armature windings of an actuator and detects the response signal to determine the position of the armature. To generate the response signal, the actuator includes a sensor excitation winding near the armature. Two sensor excitation windings can be provided, above and below the armature, to cancel out z components and thus allow for a variable gap. The sensor excitation winding or windings are supplied with an excitation signal to induce the response signal in the armature windings. The response signal is derived by differentially amplifying and frequency filtering a raw output of the armature windings. The response signal is demodulated to determine position. If a position controller rather than a mere sensor is desired, the position signal can be buffered, PID compensated, amplified, and fed back to the armature windings.
U.S. Pat. No. 6,104,328, filed on Nov. 27, 1998 entitled Resolver to 360E Linear Analog Converter and Method, is also incorporated herein in its entirety.